Control for suppressing occurrence of periodic disturbance is used in various controls such as electric power system control in receiving and transforming facilities, positioning control with robot, shaft torque resonance suppression in dynamometer system, and vibration suppression of motor housing (relating to riding comfort of a vehicle such as electric vehicle and elevator). In these applications, there is a demand for suppressing periodic disturbance accurately.
A motor, for example, produces torque ripple in principle, and thereby causes various problems such as vibration, noise, adverse influence on ride quality and electrical and mechanical resonances. Especially, in the case of an interior PM motor, there are produced cogging torque ripple and reluctance torque ripple compositely. As a countermeasure, there is proposed a periodic disturbance observer compensating method for suppressing torque ripple.
FIG. 6 is a control block diagram showing a control system for an nth order torque ripple frequency component of a periodic disturbance observer which is known from Patent Document 1, and Non-patent Document 1.
A torque ripple compensation quantity calculating section 1 generates a torque ripple compensation command Tc*n by multiplying differences between sine-wave/cosine-wave control commands rn (normally equal to zero) and estimated quantities dTA^n, dTB^n estimated by a periodic disturbance observer 3, respectively, by sine-wave/cosine-wave values, and adding the results. The torque ripple compensation quantity calculating section 1 delivers the torque ripple compensation command Tc*n to a controlled object 2. In the controlled object 2, periodical disturbance (hereinafter referred to as a periodic disturbance dTn) may be produced. In the case of a motor as the controlled object, for example, the periodic disturbance may be produced in the form of torque ripple which is disturbance synchronous with the revolution, due to cogging torque, and the periodic disturbance causes vibration and noise.
The periodic disturbance observer 3 is a device to suppress the periodic disturbance dTn. Periodic disturbance observer 3 uses a system identification model representing in terms of complex vector, for each of frequency components, and an inverse system model of the disturbance observer, and thereby estimates the disturbance of the frequency to be controlled, directly, to perform compensation.
This control configuration is relatively simple, but effective for providing high suppressing effect to target frequency without regard to the order.
To obtain the system identification model P^n, a system identification is performed to a plant Pn (=PAn+jPBn) of the controlled object, in advance of the control, and a following equation (1) is obtained in the form of one-dimensional complex vector.P^n=P^An+jP^Bn  (1)In this equation, the letter n in the subscript represents an nth order component, and each of the variables is a complex vector expressed as Xn=XAn+jXBn.
When, for example, the system identification result in the range of 1˜1000 [Hz] is expressed in the form of complex vector for each of intervals of 1 Hz, it is possible to represent the system by a table of 1000 elements of one-dimensional complex vectors. Alternatively, it is possible to represent the system by mathematical expression(s) obtained from the identification result. In either case, for a predetermined frequency component, it is possible to form a system model with a simple one-dimensional complex vector. In the explanation as well as in the system identification model, each of P^n, rn, dTn, dT^n and Tn is a complex vector expressed as Xn=XAn+jXBn.
Torque ripple is disturbance produced periodically in accordance with the rotational phase θ [rad]. Therefore, as a control of the periodic disturbance observer 3, a torque pulsating frequency component extracting means or section is used to transform to cosine coefficient TAn and sine coefficient TBn of an arbitrary order n (Integral multiple of electric rotation frequency). For strict measurement of frequency component, Fourier transform can be used. However, the system of FIG. 6 gives weight to simplicity and employs a low pass filter GF(s) as a simplified form of Fourier transform. The system causes a plant output to pass through the low pass filter GF(s), and thereby extracts a frequency component in which the periodic disturbance dTn is to be suppressed. The system multiplies this quantity by an inverse system represented by a reciprocal P^n−1 of the thus-extracted system identification model, estimates the periodic disturbance dTn from the difference the thus-determined quantity from a control command passed through a low pass filter GF(s), and delivers the estimated quantity as an estimated periodic disturbance dT^n (=dT^An+jdT^Bn), to the torque ripple compensation calculating section 1. The torque ripple compensation calculating section 1 subtracts the estimated periodic disturbance from the control command rn, and thereby suppress the periodic disturbance dTn.    Patent Document 1: WO2010/024195A1.    Non-patent Document 1: “Torque Ripple Suppression Control Based on the Periodic Disturbance Observer with a Complex Vector Representation for Permanent Magnet Synchronous Motors”, the transactions of the Institute of Electrical Engineers of Japan, D, Vol. 132, No. 1. p. 84-93 (2012).